The present invention relates to a process for controlling a distillation column which has been widely used in petrochemical industry.
Control of the distillation column has to maintain the purity of a product within a predetermined range and to suppress the loss of material due to a product from the bottom of the column. Therefore, the amount of reflux of the product at the top of the column has heretofore been controlled in response to a temperature difference between the column top and a tray in order to keep the purity of the product. Furthermore, reboiler flow rate is controlled so that the temperature at the column bottom becomes a given temperature.
However, if there are changes in the supply amount of the feed liquid and temperature, the heat equilibrium of the distillation column is lost which exerts an influence upon the product purity. Therefore, it has been attempted to control the heat equilibrium by adjusting the flow rate of the heat source from a heater. It is difficult to maintain the product purity only by manually controlling the flow rate of the heat source, due to dead time and response delay of a system.
Therefore, the distillation column is operated to reduce influences due to changes in supply of feed liquid and temperature by presetting an amount of reflux and/or the flow rate of the heat source high.
However, if the distillation process is controlled by using steam there is a disadvantage that an excess heating energy is consumed, because control is accomplished in view of a security factor.